Thermal de-polymerization process of plastic waste materials

ABSTRACT

The present invention relates to a process for producing liquid transportation fuel ( 15 ) based on plastic waste materials ( 10 ), comprising the step of: providing (S 101 ) plastic waste materials ( 10 ) in molten form; de-polymerizing (S 103 ) molten plastic waste materials ( 10 ) into a reaction chamber using a limestone catalyst ( 20 ) at a temperature ranging 420° C. to 450° C. under normal atmospheric pressure condition of 1 Bar; and introducing (S 106 ) gaseous de-polymerized products ( 25 ) to a distillation unit thereby allows the gaseous de-polymerized products ( 25 ) to be fractionally distilled and condensed into liquid transportation fuels ( 15 ).

FIELD OF INVENTION

The present invention relates to a catalytic thermal de-polymerization process of plastic waste materials. More particularly, relates to the use of a solid catalyst to convert plastic waste materials into high quality liquid fuels at a substantially low temperature without affecting yields thereof.

BACKGROUND OF INVENTION

Increasing awareness on environmental and health-related problems associated with most conventional waste plastics management methods, in which the plastic wastes has generally been burned, buried or landfilled has become a driving force to the scientists and inventors nowadays, to propose more environmentally responsible waste management solutions-pyrolysis and de-polymerization of plastic wastes.

The pyrolysis and de-polymerization processes, unlike current plastic waste disposal methods, however, have successfully recovered resources, crude oils and/or natural gas of particular, from the plastic wastes. Such waste management solutions thereby provide opportunities for the complete reuse of plastic wastes instead of degradation of such wastes in nature, where problems associated with the increasingly volume of plastics disposed in landfills remain unsolved.

An example relating to pyrolysis of waste plastic materials includes U.S. prior art document, U.S.2003047437 (A1) which teaches a two-stage pyrolysis process, in which shredded plastic wastes are initially melted and pyrolyzed into hydrocarbon oils by means of entrained inert gas from a fluidized bed with hot circulating grainy inert heat carrier at a temperature between 300° C. and 600° C. In the subsequent step, untransformed waste plastics, the heat carriers, and the entrained inert gas are separated from pyrolysis products and are subjected to the fluidized bed, where pyrolysis is completed. Pyrolysis products from the first stage and second stage are thereafter fractionated and condensed into liquid transportation fuels.

Such waste plastics pyrolysis process, as understood by one skilled in the art, has successfully alleviated limitations generally observed in fluidized bed process, for example, back mixing of pyrolysis products, non-uniformity of the fluidized bed, and more importantly low yield of valuable aromatic and high molecular hydrocarbons. However, this technology is relatively expensive since it is a multistep stage process and requires high temperature and high pressure conditions to completely decompose the plastic wastes into hydrocarbon oils. Furthermore, additional step such as removal of coke deposited on the fluidized bed by means of combustion at a temperature between 600° C. and 900° C. is required and thus contributes to a high maintenance cost.

Accordingly, thermal catalytic de-polymerization process of plastic wastes to obtain its original monomers under a milder thermal condition is rather preferred than any pyrolysis methods in the art. An example, of such thermal catalytic de-polymerization process includes U.S. patent application Ser. No. 5,369,215. This prior document discloses the use of metallic salt catalyst in depolymerization process of waste plastic derived from waste tires and rubbers, preferably which has been exposed to ozone, under a condition of elevated temperature and reduced pressure. Although the ozonized polymers are susceptible to heat, and thus allows the plastic wastes can be completely decomposed in a substantially low temperature, the deleterious effects of the ozone gaseous should not be neglected.

Therefore, it is the primary object of the present invention to overcome the aforementioned limitations associated in conventional plastic waste management methods by providing an environmentally acceptable and economically viable thermal de-polymerization process of plastic wastes.

It is yet another object of the present invention to provide a novel catalyst that allows the plastic depolymerization process to be conducted at a substantially low reaction temperature, particularly at a temperature of lower than 460° C. while not affecting yields thereof.

It is yet another object of the present invention to provide a thermal de-polymerization process that can recover high-quality liquid transportation fuels from plastic waste materials without formation of by-products, especially carbonaceous substances or cokes.

SUMMARY OF INVENTION

In one aspect of the present invention, a thermal de-polymerization process involves the use of limestone catalyst to catalytically enhance decomposition of waste plastic materials to their constituent monomers, which in turn are readily convertible into liquid transportation fuels at a temperature of below 460° C. under normal atmospheric pressure condition, is provided.

Said thermal de-polymerization process preferably comprising the steps of: providing waste plastic materials in molten form; de-polymerizing the molten waste plastic materials into a reaction chamber using a limestone catalyst at a temperature ranging from 420° C. to 450° C. range at normal atmospheric pressure condition of 1 Bar; and introducing gaseous d polymerized products to a distillation unit thereby allows the de-polymerized products to be fractionally distilled and condensed into liquid transportation fuel.

It is noted that the limestone catalyst of the present invention is a sintered product resulted from a solid composition comprising aluminum oxide (Al₂O₃) ranging from 39% to 41%; calcium oxide (CaO) ranging from 30% to 32%; silicone oxide (SiO) ranging from 0.09% to 0.12%; and magnesium oxide ranging from 0.01% to 0.03%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating the thermal de-polymerisation process of waste plastic materials so as to obtain liquid hydrocarbons therefrom, particularly transportation fuels in details.

DETAILED DESCRIPTION OF THE INVENTION

Further understanding of the object, construction, characteristics and functions of the invention, a detailed description with reference to the embodiments is given in the following.

The present invention relates to a process (100) for thermal depolymerization of waste materials, particularly plastic waste materials (10), into liquid transportation fuel (15) with the use of limestone (20) as a catalyst. The waste plastic materials (10) as described herein referred to municipal and/or industrial wastes made of, include but not limited to, polyethylene, polypropylene and polyvinyl chloride.

In one embodiment of the present invention, the limestone catalyst (20) is resulted by means of sintering a solid composition comprising aluminum oxide (Al₂O₃) ranging from 39% to 41%; calcium oxide (CaO) ranging from 30% to 32%; silicone oxide (SiO) ranging from 0.09% to 0.12%; and magnesium oxide ranging from 0.01% to 0.03%. More preferred the solid composition comprises 40.6%±0.1 aluminum oxide (Al₂O₃); 31.7%±0.1 calcium oxide (CaO); 0.15%±0.01 silicone oxide (SiO); and 0.03±0.01 magnesium oxide (MgO).

It is noted that, in addition to enhancing the depolymerization process, such limestone catalyst (20) allows plastic waste materials to be totally depolymerized into higher olefins (C₄-C₂₅) at a low temperature, preferably at temperature of below 460° under normal atmospheric pressure condition of 1 Bar. As understood, carbonization process, which leads to formation of decomposed residues or coke crystals and unacceptable environmental hazards, for example, greenhouse gases, dioxins and furans, can be suppressed with such substantially low operating temperature. Thermal depolymerization of plastic waste materials alongside with said limestone catalysts, therefore, has undoubtedly rendered the technology more economically viable and environmentally acceptable.

FIG. 1 provides the thermal depolymerization process of plastic waste materials (10) into valuable chemicals, particularly liquid transportation fuels (20) in details. Said method involves the step of depolymerizing (S103) a molten form of plastic waste materials (10) in a reaction chamber having a limestone catalyst (15) of the present invention included therein, at a temperature ranging 420° C. to 450° under normal atmospheric pressure condition of 1 Bar. It is noted that the molten plastic waste materials (10) can be prepared by heating (S101) solid plastic wastes (10) at a temperature of below 250° C. in a heated chamber. The solid plastic wastes (10) may be shredded and water content thereof is eliminated prior to being subjected to a hot melt extruder (S101).

As mentioned earlier, the limestone catalyst (15) is resulted from the step of sintering (S102) a solid composition a solid composition comprising aluminum oxide (Al₂O₃) ranging from 39% to 41%; calcium oxide (CaO) ranging from 30% to 32%; silicone oxide (SiO) ranging from 0.09% to 0.12%; and magnesium oxide ranging from 0.01% to 0.03%. In accordance to the preferred embodiment, solid composition comprises 40.6%±0.1 aluminum oxide (Al₂O₃); 31.7%±0.1 calcium oxide (CaO); 0.15%±0.01 silicone oxide (SiO); and 0.03±0.01 magnesium oxide (MgO) is pulverized and sintered (S102) to form the limestone catalyst (15) of present invention.

The depolymerization products (25), preferably a mixture of gaseous hydrocarbons, are then subjected to a distillation unit whereby allows the gaseous hydrocarbons (25) to be fractionally distilled and condensed (S106) into liquid transportation fuels (20) such as fuel diesel, kerosene and gasoline. The mixture of gaseous hydrocarbons (25) is preferably fractured (S104) at temperature ranging from 420° C. to 450° C. under normal atmospheric pressure condition of 1 Bar before the distillation process (S106). In order to have a better yield of high quality liquid fuels, a cleaning step (S105) to eliminate aerosols and particles carried by the depolymerized hydrocarbons (25) is provided. Said cleaning step (S105) preferably includes the step of guiding depolymerized hydrocarbons (25) into a pressure secure container through a high speed cyclone, thereby removing undesirable substances thereof prior to being distilled.

As discussed above, the depolymerization process (100) of the present invention not only can decompose plastic-derived waste materials (10) at a temperature ranging 420° C. to 450° C. with a cost-effective catalyst, but high quality motor vehicle fuels (20) having a cetane number of above 55 and sulfur PPM of between 0 and 50 have also been successfully recovered from waste plastic materials (10).

Although the present invention has been described with reference to the preferred embodiments and examples thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims. 

1. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) comprising the steps of: providing waste plastic materials (10) in molten form; de-polymerizing the molten plastic waste materials (10) into a reaction chamber using a limestone catalyst (20) at a temperature of lower than 460° C. under normal atmospheric pressure condition of 1 Bar; and introducing gaseous de-polymerized products (25) into a distillation unit thereby allows the de-polymerized products (25) to be fractionally distilled and condensed into liquid transportation fuels (15).
 2. A process for producing liquid, transportation. fuel (15) based on plastic waste materials (10) as claimed in claim 1, wherein said limestone catalyst (20) is resulted from sintering a solid composition comprising aluminum oxide (Al₂O₃), calcium oxide (CaO), silicone oxide (SiO) and magnesium oxide (MgO).
 3. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 1, wherein said solid composition preferably comprising aluminium (Al₂O₃) ranging from 39% to 41%; calcium oxide (CaO) ranging from 30% to 32%; silicone oxide (SiO) ranging from 0.09% to 0.12%; and magnesium oxide ranging from 0.01% to 0.03%.
 4. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 2, wherein said solid composition, more preferably, comprising 40.6%±0.1 aluminum oxide (Al₂O₃); 31.7%±0.1 calcium oxide (CaO); 0.15%±0.01 silicone oxide (SiO); and 0.03±0.01 magnesium oxide (MgO).
 5. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 2, wherein said solid composition has been pulverized prior to the sintering step.
 6. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 1, wherein step of providing molten plastic waste materials (10) comprising the steps of: eliminating water content enclosed in solid plastic wastes (10); shredding the dried solid plastic wastes (10) into pieces; and heating the dried and shredded solid plastic wastes (10) at a temperature of below 250° C. in a heated chamber.
 7. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 1, wherein said step of de-polymerizing of molten plastic waste materials (10) is preferably conducted at a temperature ranging from 420° C. to 450° C. under normal atmospheric pressure condition of 1 Bar.
 8. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 1, wherein further comprising the steps of fracturing the gaseous de-polymerized products (25) at a temperature ranging from 420° C. to 450° C. under normal atmospheric pressure condition of 1 Bar prior to being subjected to the distillation unit.
 9. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 1, wherein further comprising the step of eliminating aerosols and particles carried by the de-polymerized gaseous products (25) before the distillation step.
 10. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 8, wherein the undesirable substances of the de-polymerized gaseous products (25) can be eliminated by means of guiding the de-polymerized gaseous products (25) into a pressure secure container through a high speed cyclone.
 11. A process for producing liquid transportation fuel (15) based on plastic waste materials (10) as claimed in claim 1, wherein said liquid transportation fuel (15) characterized in that having a cetane number of above 55 and sulfur PPM of between 0 and
 50. 